The hydrolysis of nitriles has long been useful for the production of various amide intermediates in processes for making polymers such as nylon and acrylamide. Processes involving enzymatic conversion of nitrile substrates are sometimes favored over chemical synthesis, for their production of fewer harmful reaction by-products and for greater reaction specificity. The occurrence of nitrile hydrolyzing enzymes has been widely described. Within this family of enzymes, two broad classes are generally recognized. The first includes the nitrile hydratases which bring about the addition of one molecule of water to the nitrile, resulting in the formation of the amide free product: ##STR1##
The second group includes the nitrilases which bring about the addition of two molecules of water to the nitrile resulting in formation of the acid free product plus ammonia: ##STR2##
A wide range of nitriles are amenable to conversion via Reaction 1 or Reaction 2. Recent reviews have disclosed a diversity of amenable substrates for nitrile hydrolyzing enzymes found in bacterial genera such as Rhodococcus, Pseudomonas, Alcaligenes, Arthrobacter, Bacillus, Bacteridium, Brevibacterium, Corynebacterium, and Micrococcus.
The enzymatic hydrolysis of aliphatic nitriles and their derivatives by methods employing bacterial strains of the above mentioned genera is well known. For example U.S. Pat. No. 4,637,982 of Yamada et al. published Jan. 20, 1987, teaches a process for enzymatic hydration of aliphatic nitriles having 2 to 4 carbon atoms to the corresponding amide using a strain of Pseudomonas. European Patent 178 106 published Apr. 16, 1986, discloses selective transformation of one of the cyano groups of a dinitrile to the corresponding carboxylic acid, amide, ester or thioester using a mononitrilase.
Another class of nitriles that have found commercial utility in polymer synthesis are the azobisnitriles. One class of azobisnitriles of industrial interest are those capable of reacting to form organic free radicals and/or nitrogen gas, such as 2,2'-azobis (2-methylpropionitrile). These find utility as free radical polymerization initiators and/or blowing agents for polymer foams via the following reaction: ##STR3##
A disadvantage of many azobisnitriles is their low water solubility. This reduces their utility as free radical polymerization initiators and blowing agents for polymer foams in aqueous based polymer formulations. A number of chemical synthetic methods have been developed for the conversion of azobisnitriles to more water soluble derivatives. However, azobisnitriles are known to be unstable in the presence of biological organisms due to the nitrogen-nitrogen double bond. Azobis-nitriles have not been previously demonstrated to be amenable to attack by nitrile hydratase, amidase or nitrilase enzymes without reduction of the nitrogen-nitrogen double bond. Thus a need exists for converting azobisnitriles to more water soluble derivatives using enzymatic conversion to avoid the harmful reaction by-products of chemical conversions.
Applicants' invention provides a process to readily convert azobisnitriles to their cyanoamide or diamide derivatives via Reaction 1, using the enzymatic apparatus of bacteria of the genera Rhodococcus, Pseudomonas, Alcaligenes, Arthrobacter, Bacillus, Bacteridium, Brevibacterium, Corynebacterium, and Micrococcus. The enzymes may be contained within whole cells or be supplied in a semipurified or purified form. Immobilized forms of the whole cells or enzymes will also carry out the reaction.